Multimedia applications such as video streaming are delay sensitive and bandwidth intensive. Since wireless networks have limited bandwidth, the video is compressed using techniques such as MPEG-4 or H.264/AVC, which introduce the spatial and temporal dependencies within and across the video frames. As a result, the compressed video is very sensitive to the wireless channel induced packet losses as the losses introduce error propagation in the current as well as subsequent video frames leading to video quality degradation. Recent research has demonstrated the promise of cross-layer protocols for supporting the QoS demands of multimedia applications over wireless networks.
Video data can be protected against the channel errors by using forward-error-correction (FEC) schemes, which improve the successful data transmission probability and eliminate the costly retransmissions. Recently, cross-layer FEC schemes have been proposed where FEC codes are applied both at the application layer (AL) and physical layer (PHY). According to these recent proposals, equal-error-protection (EEP) or unequal-error-protection (UEP) FEC codes are applied at AL and EEP codes are applied at PHY. However, the maximum throughput does not always guarantee the minimum video distortion at the receiver. Video slices of a H.264/AVC video stream can be classified into priority classes based on the distortion contributed by their loss to received video quality. Unlike data packets, loss of H.264/AVC compressed video slices induces different amounts of distortion in the received video. Additionally, a video stream can tolerate loss of some low-priority slices because the lost slices can be error concealed and introduce low distortion in the received video, resulting in graceful quality degradation.